I'm assuming this is a problem with Session replication, or are you using jbossCache on its own? I believe Manik is just asking if the objects your putting into the cache (or your session object) implement the serializable interface, and if the key your using is also serializable. (Hopefully, a string or int?) Not sure if this helps, but look and see what your adding to the cache and if it does implement Serializable. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4029511#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...